Raising collar ties (ceiling joists)


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Old 09-25-05, 08:19 AM
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Raising collar ties (ceiling joists)

We are remodeling the 2nd floor of our cape cod style home. The collar ties are 2x4's nailed to the rafters at a height of 6' 11" from the bottom of the tie to the floor. We want to raise the ties to 8' and refinish with drywall ceiling.

First, is there any reason that raising these ties another foot is a problem?

Second, the 2x4's used as ties are are very rough and not ideal for screwing drywall to them. I was wondering if anyone had a suggestion for doing something below the ties, like perpendicular furring strips attached to the ties or someone else suggested hanging metal studs just below the wood ties on the opposite rafter and hanging the drywall to that.

Any ideas or help is appreciated.

Thanks!
 
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Old 09-25-05, 10:45 AM
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Installing collar ties at that elevation should not be a problem. However, since nailing old lumber usually causes splitting which negates structural integrity, you'd be well advised to use new lumber of sufficient size to meet span requirements.

Here is a link to a span table; http://www.awc.org/calculators/span/...rcalcstyle.asp

Be mindful of the integrity of the rafter to top plate connection when removing the existing CJ.
 
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Old 09-25-05, 11:54 AM
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I'm afraid I don't understand what you mean when you say to "be mindful of the integrity of the rafter to the top plate connection when removing the existing ceiling joist"

I was not going to nail these again (also, this is very hard wood and next to impossible to nail) - I was going to drill pilots and use lag screws as suggested in a book I read. Also, I was going to frame it in the same manor in which it was framed just 1 ft. higher.

There is a section where a dormer protrudes to the front of the house and causes the collar ties to change direction. Right now (the collar ties that I want to raise) are butt jointed into a perpendicular 2x4 that is right before the dormer. Should I count that as the end of my span for that area?

Thanks!
 
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Old 09-25-05, 09:00 PM
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[QUOTE]I'm afraid I don't understand what you mean when you say to "be mindful of the integrity of the rafter to the top plate connection when removing the existing ceiling joist"[QUOTE]

At the intersection of the RR and CT, both are nailed together. Improper or lack of caution in the removal of the CT can result in the in the disruption as well as splitting of either or both members.

[QUOTE]I was not going to nail these again (also, this is very hard wood and next to impossible to nail) - I was going to drill pilots and use lag screws as suggested in a book I read.[QUOTE]

Even with pilot holes, improperly installed lag screws can cause splitting.
I wouldn't use this method.
I would have an engineer design this connection., your family is living beneath.

[QUOTE]Also, I was going to frame it in the same manor in which it was framed just 1 ft. higher.[QUOTE]

Interesting. Collar ties help, "hold the place together", creating a two member connection, which you intend to raise, shortening the base member of the design.
You are also intending to add the additional weight of a ceiling system.
There are specific rules regarding the reuse of old lumber, some require it to be certified.
Do you intend to permit this process?

[QUOTE]Should I count that as the end of my span for that area?[QUOTE]

Yes.
 
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Old 09-26-05, 06:05 AM
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By raising the collar ties, the leverage length through which they act is severely reduced. An analogy: Hold a dining fork horizontally using only your thumb and forefinger of one hand in the middle of the fork handle. Let the end of the handle rest in the palm of that hand. Insert the tines of the fork into a biscuit. That's the collar tie in its normal placement.

Now slide the two fingers holding the fork to the end of the handle, continuing to hold the biscuit at the same height. It's more difficult using the reduced leverage. That's raising the collar ties.

Replace the biscuit with a raw potato of the same size. That's adding the sheetrock to the raised collar ties. The weight has nearly the complete length of the roof rafter to bear against the joint of the rafters against the ridge beam. That's also why truss framing is so strong - the rafter supporting the roof is more unitformly supported.

In the limiting case, having the collar tie too high is like not having one at all.
 
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Old 09-26-05, 05:40 PM
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I understand the theory on the importance of collar ties. Is there a formula to determine the maximum height. Like I said earlier, I'm not trying to vault the ceiling or anything, The bottom of the ties are at 6' 11" from the floor and I'm trying at a minimum to get the ceiling to code at 7' 6" but a little higher would be nicer.
 
 

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